The present application relates to a liquid crystal display, an optical sheet manufacturing method, and an optical sheet which make it possible to achieve an improvement in luminance and prevent the occurrence of moiré.
A liquid crystal display (LCD) realizes lower power consumption and reduced thickness in comparison to a cathode ray tube (CRT). At present, liquid crystal displays of various sizes are used for a wide variety of applications ranging from small-sized equipment such as a portable telephone and a digital camera, to a large-sized liquid-crystal television.
Liquid crystal displays are divided into a transmission type and a reflection type. A transmission type liquid crystal display, in particular, includes a liquid crystal display panel having a liquid crystal layer sandwiched by a pair of transparent substrates, and a backlight unit as an illumination light source. Backlight units include, in addition to a direct type one in which the light source is arranged directly below the liquid crystal display panel, an edge light type one using a light guide plate.
Generally, an optical sheet or film (hereinafter, generically referred to as “sheet” unless otherwise specified) having a light-condensing property, such as a prism sheet or lens sheet for orienting the outgoing direction of light from a light source to the front direction, is used for the backlight unit for a liquid crystal display. For example, a prism sheet has a large number of prisms having a triangular cross section arranged on the light-emergent side surface, and causes light incident on the prism sheet to be refracted by and transmitted through the slopes of the prisms, thereby condensing the light into the front direction.
Meanwhile, light-dark fringes (moiré) occur due to the interference of light between the prism arrangement pitch of the prism sheet and the pixel arrangement pitch of the liquid crystal display panel. It is known that narrowing the prism arrangement pitch (to 100 μm or less, for example) proves effective in preventing the occurrence of such moiré.
Further, the occurrence of moiré due to the interference of light between the prism arrangement pitch and the pixel pitch can be prevented by arranging a diffuser sheet between the prism sheet and the liquid crystal display panel (Japanese Unexamined Patent Application Publication No. 6-102506).
However, the method of simply narrowing the prism arrangement pitch leads to a significant decrease in front luminance, resulting in a deterioration of image quality.
Further, with the method of arranging a diffuser sheet between the prism sheet and the liquid crystal display panel, depending on the characteristics of the diffusion film, there may be cases where the light beams condensed by the prisms cannot be effectively utilized, making it impossible to attain an intended luminance improving effect.